1. Technical Field
The present disclosure relates generally to an uninterruptible power system a method of operating the same, and more particularly to an uninterruptible power system with a function of backfeed failure detection and a method of operating the same.
2. Description of Related Art
Uninterruptible power supply (UPS), as the name indicates, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails. Because the UPS is more complicated and more expensive than other emergency power apparatuses, the UPS is usually provided to protect important equipment, such as computer equipment, monitor instruments, fire equipment, medical instruments, and so on, thus achieving strict power requirements for the above-mentioned equipment and instruments. In addition, the UPS also provides voltage adjustment once the over-voltage or the under-voltage conditions occur. Furthermore, the UPS can provide good effect for restraining transient fluctuation and harmonic disturbance.
Reference is made to FIG. 1A which is a system block diagram of a related art uninterruptible power system operating in a backup supply operation. The uninterruptible power system mainly includes a two-stage power converter 10A, a static transfer switch 11A, a current sensor 12A, a voltage detector 13A, and a controller 14A. The uninterruptible power system receives an AC power source Vac and the two-stage power converter 10A converts the AC power source Vac into an AC output voltage to supply power to an AC load Ld. In particular, the two-stage power converter 10A has an AC-to-DC conversion circuit (not shown) and a DC-to-AC conversion circuit (not shown). Also, a rechargeable battery (not shown) and a charging circuit (not shown) are provided. When the AC power source Vac is disabled, the AC load Ld is supplied by the rechargeable battery. As shown in FIG. 1A, an output voltage of the static transfer switch 11A can be detected by the voltage detector 13A when the static transfer switch 11A is in a normal operation. Afterward, a voltage signal is sent to the controller 14A.
However, the stored energy of the rechargeable battery is fed back to the input terminal of the uninterruptible power system once the static transfer switch 11A is in an abnormal operation because two input terminals are shorted. In this condition, the uninterruptible power system must execute the shutdown protection. Reference is made to FIG. 1B which is a system block diagram of the related art uninterruptible power system operating in a backfeed failure operation. The current sensor 12A, which is usually the current transformer, is used to detect the current flowing through the bypass path. The backfeed failure occurs when the static transfer switch 11A is in an abnormal operation because two input terminals are shorted. In this condition, not only the voltage detector 13A detects the output voltage Vo but also the current sensor 12A simultaneously detects a great magnitude of current. Afterward, a current signal is sent to the controller 14A. The controller 14A confirms that the static transfer switch 11A is in the abnormal operation to cause the backfeed failure according to the voltage signal and the current signal.
However, the malfunctions of the current transformer would easily occur due to interruption of the large-current detection even if the uninterruptible power system is in the normal operation. Hence, the controller 14A wrongly detects that the backfeed failure occurs so that the uninterruptible power system must execute the shutdown protection.
Accordingly, it is desirable to provide an uninterruptible power system with a function of backfeed failure detection and a method of operating the same so as to achieve advantages of reduction in costs, simplicity of circuit designs, and utilization of occupied space, further significantly reduce malfunctions and increase accuracy of detecting the backfeed failure.